There are different ways to tackle this. Voltage regulators will keep the voltage at a target voltage (but require a higher input voltage). If your input voltage doesn't vary much and is at a known value and you're not going to be pulling a lot of amps, you could just use some resistors (make a voltage divider), although this isn't necessarily efficient. I'm not really an electronics guy, though.

Here check this video out. The guy here talks alot about voltage dividers and regulators and how one is or is not better than another. It also shows you schematics that will allow you to build your own pretty easily.